W.S. Chan

Radiosity method: a new propagation model for microcellular communication

We discuss the development of a new three-dimensional model applicable for characterizing the propagation characteristics for microcellular communications. For microcellular communication, the working frequency is about 1.7-2.0 GHz. The wavelength is about 15-18 cm. In essence, these wavelengths are comparable with the dimensions of cavities such as windows, balconies, etc. on buildings. Thus multiple reflection and diffraction might occur inside or on the surface of the cavities, rendering that reflections resemble the diffuse type, in a macroscopic perspective. In such circumstances, employing the diffuse reflection model is more efficient than the specular reflection model. Hence, the radiosity method is employed. The radiosity equations, and hence the radiosity parameters and form factors, are rederived in a style that are suitable for electromagnetic wave application. We then formulate our own model for analysis and derive the path loss expression.

Design of optimized circular sectors for ultra-wideband patch antenna

An UWB patch antenna design based on optimized circular sectors is presented. The shape modeling of the antenna is based on a number of small circular sectors. In this structure, the shape of the antenna varies with the antenna parameters. This results in a highly tunable structure that is suitable for different design requirements. The optimization objectives are based on the VSWR, antenna size, radiation pattern and gain. The optimized antenna achieved VSWR ≤ 2 with omni-directional pattern, which satisfy the basic requirements of UWB antenna.

Broadband parallel stubs phase shifter

This paper presents a parallel stubs structure with simple matching network which can provide a constant differential phase shift using uniform transmission lines that can realise a wide bandwidth of more than 120%. For demonstration purposes, two broadband phase shifters are designed, fabricated, and measured to give excellent performance for wireless local area network and ultra wide band applications respectively.

Wideband circular polarized antenna with a slot composed of multiple circular sectors

Circular polarized antenna is an important component in satellite communication. There are many designs in the literature for improving the return loss as well as the axial ratio bandwidth of the antenna [1 – 4]. A dual-feed structure can provide a wideband characteristic for circular polarized antenna design [1, 2]. However, the size of the antenna becomes larger with the inclusion of the broadband power divider with quadrature phase distribution. The single feed circular polarized antennas [3, 4] have narrower bandwidths compared with the dual-feed designs but with simpler structures. A recent design of wideband circularly polarized antenna with L-shaped slot [4] can provide 46.5 % bandwidth. In this paper, we are going to extend the bandwidth further by replacing the L-shaped slot with a slot composed of multiple circular sectors. A similar approach for designing an ultra-wideband antenna with multiple circular sectors has already been proposed in [5].

Broadband 3dB hybrid coupler with flat coupling designed by Jumping Genes Evolutionary Algorithm

A compact slot-coupled broad band 3 dB hybrid coupler has been designed and implemented. Compensation sections are added to achieve a flat coupling without significantly enlarging the size of the coupler. Optimization base on Jumping Genes Evolutionary Algorithm is performed to obtain a tight coupling within 1 dB imbalance over the band 1.8 - 5.7 GHz.

An ultra-fast locking frequency synthesizer algorithm for zero blind slot communication in Digital European Cordless Telephone (DECT)

This paper presents the algorithm of a fast locking phase locked loop frequency synthesizer designed for the (1.9 GHz) Digital European Cordless Telephone (DECT) system. Off-line reload and open loop modulation techniques were adopted. The frequency synthesizer can lock at any DECT channel within the 48 microseconds guard time. It can provide the capability of zero blind slot operation for the DECT system. This paper gives an account of the design of a fast acquisition frequency synthesizer which yields a high spectral purity and a wide tuning range. With minor modifications, the proposed algorithm can be adopted to other digital cellular applications.

High Tc superconductor harmonic mixer at W-band

Using high Tc superconductor Josephson junctions, a harmonic mixer at W-band has been realized. A local oscillator frequency of 43 GHz is used to down-convert a signal frequency of 96 GHz to an intermediate frequency of 10 GHz. The tangential sensitivity of the mixer was measured to be about -40 dBm.